Devices for stirring liquids are generally known, in which the surface of an appliance base containing a magnetic-field generating system has placed on it a stirring vessel, in which the liquid to be treated is introduced and a magnetic stirring rod is inserted, which interacts with a rotating magnetic driving field generated by the magnetic-field generating system of the appliance base and which stirs the liquid.
In specific instances of use, it may be expedient to avoid the difficulties arising as a result of the separate handling of the stirring rod and the wetting of the latter by the liquid to be treated.
German Utility Model G9406540.4 discloses a magnetic stirring device which, in a plate-shaped base, contains a number of magnetic-field generating systems which generate rotating magnetic fields near the top side of the base. Located on the top side of the base are rotatably mounted vessels, for example in the form of test tubes, which have, near their lower end, a holder containing a magnetic member, the said holder being supported in each case with a bearing pivot point against a step bearing on the top side of the base. The vessels are rotatably mounted near their upper end on a carrier, in such a way that the vessels can be set in rotation by means of the magnetic members which interact with the magnetic rotary fields. If the vessels are driven at a changing rotational speed or in the direction of rotation which, for example, changes periodically, liquid introduced into the vessels undergoes intimate intermixing due to the shearing forces acting in it, since liquid located in the treatment vessel is entrained in the layers adhering to the vessel inner wall, whereas the parts of the liquid volume which are near the axis lag behind during rotation.
It is apparent that the pivot point mounting of the lower vessel end of the holder attached onto the lower vessel end in a bearing depression ensures that a vessel runs centrically in its lower part within a wide rotational speed range, but that the rotary mounting near the upper vessel end tends to run unevenly because of the comparatively large diameter of the vessel, and that undesirable rattling phenomena occur which may ultimately cause the vessel to stop if the driving torque of the magnetic-field generating system is no longer sufficient. A reduction in the bearing play of the upper rotary mounting presents difficulties on account of the tolerances in the diameter of the vessels and may put at risk the smooth movement of the rotary mounting of the vessel as a whole. Undesirable rattling phenomena of the upper rotary mounting are triggered by small unbalances [lacuna] is pressed against a point region of the bearing bore by the centrifugal forces against the vessel outer wall, and the vessel begins to roll on the bearing-bore inner wall under the driving force.